PSU information science scholar Jim Jansen was guest editor for a special issue of the Bulletin for the American Society for Information Science and Technology on the practice of paid search.
Jim was kind enough to ask me for a contribution on the ethical implications of paid search. My brief contribution, “The Value Implications of the Practice of Paid Search,” warns of the potential value implications of the practice of paid inclusion and paid placement of sites within search engine results, focusing on three interrelated values of moral and ethical import: freedom from bias, privacy and trust. It closes with a call to action for the search engine and paid search community to engage in value-sensitive design to ensure such values are protected in the conception and design of these important and powerful knowledge tools, rather than being merely retrofitted after completion.
Jim’s post on the special issue is here.
MichaelZimmer.org 
Good points about the ethics of paid inclusion. But to be fair, paid inclusion is often cheaper than similar CPC/CPM campaigns. Paid inclusion is more to the benefit of the advertiser than the searcher.